Nate Silver is convinced it's 'all of the above" when it comes to the various theories as to why Sarah Palin really quit her day job.
From Nate Silver:
There seem to be three* basic theories to explain why Sarah Palin decided to quit:
1. She's simply burned out;
2. There's some kind of "other shoe dropping";
3. She's so crazy she thinks this could actually help her for 2012, 2016, etc.
The point I'd add is that I don't think these three things are mutually exclusive. In her press conference today, Palin didn't seem sure of much of anything except that she'll no longer be governor. She may have felt like being governor of Alaska had become a waste of her time when she can go about the country being a celebrity instead; she might have concerns for what the national media spotlight has done to her family; she might be worried that she's made too many enemies in the state and that sooner or later one of these mini-scandals will blow up into a bigger one ... AND she may be crazy and narcissistic enough to think this will actually help her chances for 2012.